$ 160. THE ANNELIDES. 178 
arranged loops. " With Lumbricus, these aquiferous canals are sur- 
rounded by a very distinct vascular net-work, which has a botryoidal 
aspect from its numerous pedunculated, vesicular dilatations which are filled 
with blood.® - 
§ 160. 
With most of the Capitibranchiati, and Dorsibranchiati, the respiratory 
organs consist of external branchiae, which are very apparent, although 
having variations in their development. They always consist of lobules or 
filaments covered with ciliated epithelium, and in which are very con- 
siderable vessels as branchial arteries and veins. The branchiae are 
here always situated between the venous and arterial systems, so that a 
portion only of the whole blood is made to pass through the respiratory 
organs. 
qt is possible that the two bundles of tentacles which are found with 
many Capitibranchiati, as infundibuliform,” or spiral® tufts, are also res- 
piratory; for their vibratory organs not only draw in food, but also pro- 
duce a constant change of the water. 
Other Capitibranchiati have distinct and exclusively respiratory organs 
in the cervical region, which are either dendritic,” or semi-pinnate. 
With the Dorsibranchiati, nearly every segment of the body ‘has branchiae 
upon both sides of its dorsal surface. 
These are so simple and rudiment- 
ary with the Ariceae, and Nereideae, that they consist only of simple lob- 
ules, exactly resembling the cirri of the feet. 
Enchytraeus albidus, and others. Those canals 
thus situated remind one of the trembling organs 
of Rotatoria, connecting the two lateral canals 
with the cavity of the body ; see above, § 138. 
6 With Lumbricus terrestris, and its allied 
species, I have as yet been unable to find any ori- 
fices of the aquiferous canals. Henie also (Miul- 
ler’s Arch. 1835, p. 580) has always found them 
looped upon themselves. They may however exist, 
although they have eluded-the notice of Hende and 
myself, for the respiratory organs of Lumbricus 
are so difficult to study that there is yet no de- 
scription or figure giving any idea of their com- 
plexity ; see the poor figures of Lumbricus ter- 
restris by Leo (loc. cit. p. 25, Tab. I. fig. 4), and 
Morren (loc. cit. p. 53, 148, Tab. XIV. XV). 
Those of Hoffmeister, although more detailed, are 
scarcely less unsatisfactory (loc. cit. p. 15, Tab. I. 
fig. 35, 36). It now remains to inquire as to the 
relations existing between these aquiferous canals 
and the glands at their base which have been 
taken by many for mucous pouches, I cannot, for 
my own part, perceive that these glands with the 
Lumbricus terrestris, excrete any liquid what- 
ever upon the ventral surface. On the other haad, 
I have often seen escape from the back of this 
animal, a watery liquid which was only the con- 
tents of the cavity of the body, issuing through 
small orifices upon each side of the median line 
between the segments of the body. Although I do 
not know, yet I suppose, that similar orifices exist 
with the other Lumbricini, and thus, by these ori- 
fices and by those of the internal branchiae, the 
necessary renewal of water for these last, can take 
place. This hypothesis appears admissible since 
the cilia of the aquiferous canals always move in 
the same way. 
*[§ 159, note 7.] See, for many details on 
these parts, Gegenbaur (Ueber d. sogenannten 
15* 
7 These vesicular dilatations do not pulsate, and 
are undoubtedly analogues of the simple sinuses 
which communicate with the aquiferous canals of 
Nephelis vulgaris.* 
1 These respiratory organs may be taken as 
analogous to the aquiferous vessels of the Lumbri- 
cini, which can be everted so that the internal cil- 
iated surface becomes external, and the external 
blood-vessels internal. 
2 Serpula, and Protula. 
3 Sabella. 
4 Terebella; see Delle Chiaje, Mem. loc. cit. 
Tay. XLIII. fig. 1-5, Tav. XLV. fig. 2,10; and 
Milne Edwards, Ann. d. Sc. Nat. X. 1838, p. 200, 
PL. X. XI. fig. 1. There are here on each side of 
the neck three multiramose, contractile branchiae 
which are placed close together. Into these a 
large portion of the blood of the median dorsal ves- 
sel enters by six lateral branches, while the re- 
maining portion passes on through the dorsal ves- 
sel to the tentacles and the borders of the lips. 
In each branchial tuft there are a simple artery 
and a vein placed side by side, which anastomose 
at its extremity in an arcuate manner. 
The returning blood from the six branchiae 
passes by as many veins into the median dorsal 
vessel, and the frequent strong contractions and 
dilatations of the branchiae, certainly very much 
aid the current. 
5 Amphitrite, see Pallas, Miscell. zool. p. 120, 
Tab. IX. fig. 1, 5, 6, 8, e,e3; Rathké, Danzig. 
Schrift. loc. cit. p. 59, Taf. V. fig. 1,3. Here the 
four semi-pinnate branchiae are upon both sides of 
the second and third rings of the body, and each 
lamella contains a tightly-closed vascular net- 
work. 
6 The fil 
of these br 
are very short 
Respir ) genwurms, in Siebold 
and Kélliker’s Zeitsch. IV. p. 221). — Ep. 
gane d. R 
